1. Field of the invention
The present invention relates to a pipe feeding mechanism of an automatic pipe bender, more particularly one, which can deliver great output force when feeding a pipe through a bending mechanism, and can move back to the initial position-at higher speed after it finishes feeding the pipe.
2. Brief Description of the Prior Art
Referring to FIGS. 4, and 5, a conventional pipe bender includes a main holding portion 10, a feeding mechanism 20 movable on the main holding portion 10, a power source (not shown), and a bending mechanism, which is comprised of a stationary arm 30, a movable arm 40, and an actuating shaft 401 connected with both the movable arm 40 and the power source. The feeding mechanism 20 is provided for feeding a pipe secured thereto through the bending mechanism, and the movable arm 40 will be displaced relative to the stationary arm 30 to bend the pipe by the power source after the pipe is held in position on the arms 30 and 40. The arms 30 and 40, and molds to be used together with the arms 30, 40 for bending a pipe are not the subject of the present invention therefore they are not detailed herein. The feeding mechanism 20 will move back to the initial position after it finishes feeding a pipe into the bending mechanism for allowing the next pipe feeding cycle to start.
Feeding mechanisms of pipe benders have to deliver great output force in feeding a pipe into bending mechanisms of pipe benders, and are usually equipped with planetary gears, through which great output force can be provided. Referring to FIG. 6, feeding mechanism 20 is movably supported on a main holding portion 10 (FIGS. 4, and 5) of a pipe bender, and comprised of a power source 201, and a planetary gear set 202. The planetary gear set 202 includes a fixed sun gear 204, an input shaft 2021 arranged in the sun gear 204 and securely connected with an output shaft 2011 of the power source 201, several planet pinions 2022, and a rotary shaft 203, and a gear 2031 secured to a lower end of the rotary shaft 203 and engaged with a rack 101 fixedly disposed on the main holding portion 10. The sun gear 204 has gear teeth on an inner side thereof. The planet pinions 2022 are rotary on respective shafts 2023 supported in position on the rotary shaft 203, and are engaged with both the input shaft 2021 and the toothed inner side of the sun gear 204; thus, when the input shaft 2021 is made to turn by the power source 201, the planet pinions 2022 will rotate on respective shafts 2023, and make circular motion around the input shaft 2021. Therefore, when the power source 201 functions, the rotary shaft 203 is turned owing to the circular motion of the planet pinions 2022, and in turns, the feeding mechanism 20 moves left and right along the rack 101 while the pushing force of the mechanism 20 is increased owing to the planetary gear set 202 functioning to reduce the speed.
The feeding mechanism 20 will push a pipe through a bending mechanism with increased force and reduced speed in the feeding stroke owing to the planetary gear set 202. However, the feeding mechanism will also move at the same speed during the back stoke due to the planetary gear set 202, and it's a waste of time because there is no need for the planetary gear set to function to increase the output force during the back stroke of the feeding mechanism 20. Consequently, efficiency of the pipe bender is reduced.